Different materials, MUCH better harness on the Zip. No frame (none needed) and it's smaller volume wise than even the Miniposa. Ron lifted the "Y" strap from GG, though :-)>.
There is a form factor that GG, MLD, Fanatic Fringe, Six Moons, etc. share----top loading, roll up closure, tall and narrow, provision for shock cord compression, mesh pockets. It's a combo that works well for most UL and SUL packs.